When a hydraulic motor for driving an inertia member is stopped, first and second main circuits connected to first and second ports of the hydraulic motor are shut off by brake valves. However, in such case, since the hydraulic motor is rotated by an inertia force of the inertia member to thereby cause a pumping function which causes a cavitation to one of the first and second main circuits, the first and second main circuits are communicated through a relief valve so that a pressure oil drained from one of the ports flows, through the pumping function of the hydraulic motor, to the other one of the ports to smoothly stop the hydraulic motor.
However, when the hydraulic motor is stopped by the manner mentioned above, an elastic energy is stored to a connection shaft connecting the hydraulic motor and the inertia member at the hydraulic motor stopping time, the hydraulic motor is reversely driven by the elastic energy, and the hydraulic motor is then stopped through the repetition of such operation. That is, a reverse rotation phenomenon due to reaction or rebound force caused at this time is generated, this phenomenon being called herein a rebound reverse rotation phenomenon.
For the reason described above, for example, as disclosed in Japanese Patent Laid-open Publication No SHO 57-25570, there is provided a reverse rotation preventing apparatus for preventing the rebound reverse rotation phenomenon by disposing reverse rotation preventing valves to the first and second main circuits, respectively, in a manner that when a pressure in one of the main circuits exceeds a preset pressure, a high pressure oil flows to the other one of the main circuits.
According to such reverse rotation preventing apparatus, since the high pressure oil in one of the main circuits is merely drained to the other one thereof, much time is taken up to the time when the pressures in the first and second main circuits are lowered, and hence, much time is also taken up to the time when the rebound reverse rotation phenomenon is settled. That is, the hydraulic motor is much reversely rotated till the operation of the hydraulic motor stops.
As mentioned above, the fact that much time is taken up to the settling of the rebound reverse rotation phenomenon means that much time is also taken up from the starting of the hydraulic motor stopping operation to the actual stopping thereof. Accordingly, when applied to a hydraulic power shovel, a time interval required from the swinging time of the upper revolving member to an excavation starting time is made long, lowering a working efficiency.
Therefore, the present invention aims to provide an apparatus for preventing a reverse rotation of a hydraulic actuator capable of making short a time interval up to the settling of the rebound reverse rotation phenomenon when a hydraulic actuator such as hydraulic motor is operated to stop the same.